A PON (Passive Optical Network) is a point-to-multipoint optical network architecture. The PON may for instance be a Fiber to the Premises, Fiber to the Curb, Fiber to the Cabinet or Fiber to the Building network. Unpowered optical splitters are used to enable a single optical fiber to serve multiple sites.
A PON consists of an OLT (Optical Line Terminal) at the service provider's CO (Central Office) and a number of ONUs (Optical Network Units) near end users. The PON configuration reduces the number of optical fibers required and cost compared with point to point architectures. Downstream signals are transmitted to and upstream signals are received from each premise sharing a single fiber by using a multiple access protocol such as TDMA, Time Division Multiple Access or WDM, Wavelength Division Multiplexing.
There are several well-established standards for PONs, like GPON. New technologies are also being developed which increase the available bandwidth per user. Development of these new technologies is among others driven by the never-ending bandwidth thirst for large volume data transmissions and HDTV-streaming. One of these new solutions is hybrid WDM/TDM-PON systems which use both WDM and TDM as multiple access protocol. WDM/TDM-PON systems enable a higher number of users to be connected to one access network infrastructure. There have been several approaches towards WDM/TDM-PON solutions. Some of them include tunable elements at the ONU, which is still an expensive technology in the access network. A great potential has been discovered in RSOA, Reflective Semiconductor Optical Amplifiers, and REAM, Reflective Electro Absorption Modulators. Although they are sufficiently wavelength-agnostic, they still have serious drawbacks. RSOA has a limited modulation bandwidth (max 2.5 GHz) and the REAM suffers from very high intrinsic loss and requires an optical amplifier.
There is therefore a need for an improved solution for WDM/TDM-PON, which solution solves or at least mitigates at least one of the above mentioned problems.